property line vs boundary line

property line and boundary line both are nouns.

Word	Noun	Adjective	Verb	Adverb
property line	Yes	No	No	No
boundary line	Yes	No	No	No

As nouns, boundary line is a hypernym of property line; that is, boundary line is a word with a broader meaning than property line:

Other hypernyms of property line include border, borderline, delimitation, mete.

property line (noun)	boundary line (noun)
the boundary line between two pieces of property	a line that indicates a boundary